Sickle cell disease (SCD) when included with other hemoglobinopathies (?- and ?-thalassemia) are the most common inherited diseases in man, and most often patients require treatment for their entire lives. Current treatment modalities either have debilitating side effects or are not effective for a major subset of affected individuas. The annual cost of medical care of SCD patients in the US alone exceeds $1.1 billion/annum (ca. 2008). Both clinical and experimental studies have found that even a modest increase in ?-globin expression can alleviate symptoms, organ pathology, and pain in SCD. Our laboratory identified a macromolecular repressor complex responsible for repression of the ?- and ?-globin genes, and the core DNA binding components of this complex are the orphan nuclear receptors TR2 (NR2C1) and TR4 (NR2C2). When this repressor complex is inhibited, the expression of ?-globin increases and the pathophysiological manifestations of SCD were reduced, thus making it an attractive target for therapeutic development. However, other than the ?- and ?-globin gene the transcriptional targets and genome-wide binding of all dimeric receptor species (i.e. TR2 homodimer, TR4 homodimer, or TR2/TR4 heterodimer) or the actions by which each species activates or represses erythroid transcription (e.g. their differential association with co-activatrs and co-repressors) are largely unknown. Our overarching hypothesis is that TR2 and TR4 homo- and heterodimers form distinct transcriptional complexes to either activate or repress target gene transcription during erythroid differentiation. Specific aim 1 will examine the direct genomic binding sites and transcriptional targets of TR2- and TR4- homodimers and heterodimers through a ChIP-seq approach in stage purified murine erythroid progenitor cells, and utilization of fused dimers to examine specific dimer activity. In Specific aim 2, we will examine the mechanisms that direct the binding of TR2 and TR4 homodimers and heterodimer complexes to DNA in erythrocytes. The discoveries from this project will provide a deeper understanding of the functions of TR2 and TR4 during normal erythropoiesis, and provide a better understanding of the molecular mechanisms controlling globin gene expression; in turn, these findings will aid in the development of new therapeutics with greater specificity and fewer negative side effects than current medications used to treat the hemoglobinopathies.